A record of sea surface temperatures from the tropical Pacific implies that atmospheric greenhouse gases caused the duration of glacial cycles to increase from 41,000 to about 100,000 years 950,000 years ago.

About The Cover

COVER Fossil leaf from the earliest Eocene (~55.5 million years ago) of the Bighorn Basin, Wyoming. The beginning of the Eocene was characterized by rapid global warming after a huge release of carbon into the atmosphere and ocean. Plant fossils described on page 993 document rapid, continental-scale changes in the geographic ranges of plants coincident with the warming. [Photo: S. Wing]